U.S. patent number 8,179,328 [Application Number 12/355,431] was granted by the patent office on 2012-05-15 for direction finding antenna.
This patent grant is currently assigned to Astron Wireless Technologies, Inc.. Invention is credited to Glenn F. Brown.
United States Patent |
8,179,328 |
Brown |
May 15, 2012 |
Direction finding antenna
Abstract
Systems and methods provide a HESA ("High Efficiency Sensitivity
Accuracy") direction-finding ("DF") antenna system that operates
over a range from 2 MHz to 18 GHz. The system may include
components such as a dipole array, a monopole array, and an
edge-radiating antenna, each component being responsive to a
specific frequency range. The system may further include biconical
flares that optimally terminate a freespace wave in a small
aperture.
Inventors: |
Brown; Glenn F. (Fairfax,
VA) |
Assignee: |
Astron Wireless Technologies,
Inc. (Sterling, VA)
|
Family
ID: |
41088363 |
Appl.
No.: |
12/355,431 |
Filed: |
January 16, 2009 |
Prior Publication Data
|
|
|
|
Document
Identifier |
Publication Date |
|
US 20090237318 A1 |
Sep 24, 2009 |
|
Related U.S. Patent Documents
|
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
|
61037941 |
Mar 19, 2008 |
|
|
|
|
Current U.S.
Class: |
343/725; 343/820;
343/816; 343/810; 343/773; 343/891 |
Current CPC
Class: |
H01Q
13/04 (20130101); H01Q 21/062 (20130101) |
Current International
Class: |
H01Q
21/00 (20060101); H01Q 13/00 (20060101) |
Field of
Search: |
;343/725,773,810,816,820,890,891 |
References Cited
[Referenced By]
U.S. Patent Documents
Other References
International Search Report and Written Opinion in
PCT/US2009/037457, dated May 18, 2009. cited by other.
|
Primary Examiner: Nguyen; Hoang V
Attorney, Agent or Firm: Womble Carlyle
Parent Case Text
RELATED APPLICATION
This application claims priority to provision application No.
61/037,941 filed Mar. 19, 2008.
Claims
What is claimed is:
1. A direction-finding antenna with electronics for receiving radio
signals in a frequency range of about 2 megaHertz to about 18
gigaHertz, said direction-finding antenna comprising: an
edge-radiating antenna comprising a first plate and a second plate
disposed parallel to each other and radiating into open space, a
concentric cylinder connecting the first plate to the second plate,
eight feed points disposed equally around the outside of the
concentric cylinder with eight feed lines extending from the first
plate to the second plate, and a shunt resistor across each feed
gap, wherein the eight feed lines are electrically coupled to a
first beam forming matrix that finds a direction of a beam; a
monopole array comprising eight monopole elements connected to a
first center mast, wherein the monopole array is disposed inside
the concentric cylinder and resistively modified such that no
resonance occurs, and wherein the eight monopole elements are
electrically coupled to a second beam forming matrix that finds a
direction of a beam; a dipole array comprising eight dipole
elements connected to a second center mast, wherein each of the
eight dipole elements is resistively loaded to increase bandwidth,
and wherein the eight dipole elements are electrically coupled to a
third beam forming matrix that finds a direction of a beam; and a
first and second biconical horn housing the edge-radiating antenna
and dipole array, respectively, the first and second biconical horn
each comprising eight ribs connecting a top horn to a bottom horn,
wherein the eight ribs are electrically couple to a high impedance
resistor disposed at the center of the biconical horn.
2. The direction finding antenna of claim 1, wherein the direction
finding antenna is modular such that the edge-radiating antenna may
be decoupled from the dipole array.
3. The direction finding antenna of claim 1, wherein the top horn
and bottom horn of the first and second biconical horns each
includes a base having an aperture termination including resistors
in shunt with each other.
4. The direction finding antenna of claim 1, wherein the second
center mast includes a plurality of resistors disposed on the mast
to prevent resonance.
5. The direction finding antenna of claim 1, wherein the first,
second and third beam forming matrices each comprise: eight inputs;
a sine pattern output; a cosine pattern output; and an omni
directional pattern output.
6. The direction finding antenna of claim 5, wherein the eight
inputs include inputs A, B, C, D, E, F, G and H, and the sine
pattern equals (input C+input D)-(input G+input H).
7. The direction finding antenna of claim 5, wherein the eight
inputs include inputs A, B, C, D, E, F, G and H, and the cosine
pattern equals (input A+input B)-(input E+input F).
8. The direction finding antenna of claim 5, wherein the omni
directional pattern is the sum of the eight inputs.
9. The direction finding antenna of claim 5, wherein the sine,
cosine, and omni directional patterns are used to calculate a
direction of a beam.
10. A direction finding edge-radiating antenna comprising: a first
plate and a second plate disposed parallel to each other and
radiating into open space; a concentric cylinder connecting the
first plate to the second plate; eight feed points disposed equally
around the outside of the concentric cylinder with eight feed lines
extending from the first plate in the direction of the second
plate, each feed point having a feed gap; and at least one shunt
resistor across each feed gap, wherein the eight feed lines are
electrically coupled to a first beam forming matrix that finds a
direction of a beam, and wherein the direction finding
edge-radiating antenna operates in a first band.
11. The direction finding edge-radiating antenna of claim 10, in
combination with: a monopole array comprising eight monopole
elements connected to a center mast, wherein the monopole array is
resistively modified such that no resonance occurs, and wherein the
eight monopole elements are electrically coupled to a second beam
forming matrix that finds a direction of a beam; wherein the
monopole array and center mast project axially outside the
concentric cylinder and operate in a second band different from the
first band.
12. The direction finding edge-radiating antenna of claim 10,
wherein the first and second beam forming matrices each comprise:
eight inputs; a sine pattern output; a cosine pattern output; and
an omni directional pattern output.
13. The direction finding edge-radiating antenna of claim 12,
wherein the eight inputs include inputs A, B, C, D, E, F, G and H,
and the sine pattern equals (input C+input D)-(input G+input
H).
14. The direction finding edge-radiating antenna of claim 12,
wherein the eight inputs include inputs A, B, C, D, E, F, G and H,
and the cosine pattern equals (input A+input B)-(input E+input
F).
15. The direction finding edge-radiating antenna of claim 12,
wherein the omni directional pattern is the sum of the eight
inputs.
16. The direction finding edge-radiating antenna of claim 12,
wherein the sine, cosine, and omni directional patterns are used to
calculate a direction of a beam.
17. The direction finding antenna of claim 12, wherein the sine,
cosine, and omni directional patterns are used to calculate a
direction of a beam.
18. A direction finding antenna, comprising: a dipole array
comprising eight dipole elements connected to a center mast,
wherein each of the eight dipole elements is resistively loaded to
increase bandwidth; and a beam forming matrix that finds a
direction of a beam electrically coupled to the dipole array,
wherein: the center mast includes a plurality of resistors disposed
on the mast to prevent resonance.
19. The direction finding antenna of claim 18, wherein each dipole
element is disposed one quarter wavelength away from the center
mast at the highest operating frequency and one half wavelength
apart on the circumference of the array.
20. The direction finding antenna of claim 18, wherein the beam
forming matrix comprises: eight inputs; a sine pattern output; a
cosine pattern output; and an omni directional pattern output.
21. The direction finding antenna of claim 20, wherein the eight
inputs include inputs A, B, C, D, E, F, G and H, and the sine
pattern equals (input C+input D)-(input G+input H).
22. The direction finding antenna of claim 20, wherein the eight
inputs include inputs A, B, C, D, E, F, G and H, and the cosine
pattern equals (input A+input B)-(input E+input F).
23. The direction finding antenna of claim 20, wherein the omni
directional pattern is the sum of the eight inputs.
24. A biconical horn antenna, comprising: an antenna; a top horn; a
bottom horn; eight ribs connecting the top horn to the bottom horn,
wherein: each of the eight ribs includes a feed point which
connects to a beam forming matrix, and each of the eight ribs is
electrically coupled to an associated high impedance resistor
belonging to a resistor array disposed at the center of the
biconical horn antenna.
25. The biconical horn antenna of claim 24, wherein the top horn
and bottom horn each includes a base having an aperture termination
comprising resistors in shunt with each other.
26. The biconical horn antenna of claim 24, further comprising: a
first array of low frequency resistors attached to the top horn;
and a second array of low frequency resistors attached to the
bottom horn.
27. The biconical horn antenna of claim 24, wherein the beam
forming matrix comprises: eight inputs; a sine pattern output; a
cosine pattern output; and an omni directional pattern output.
28. An On-the-Move antenna, comprising: a base; four dipole
elements attached to the base, each dipole element including first
ferrite beads and a first resistor between a feed point and the
base; a beam forming matrix electrically coupled to the four dipole
elements, wherein the beam forming matrix determines a direction of
a signal.
29. The On-the-Move antenna of claim 28, wherein each dipole
element further comprises: second ferrite beads located at the
base, wherein the second ferrite beads are larger than the first
ferrite beads.
30. The On-the-Move antenna of claim 28, further comprising: a
second resistor located near an end of each dipole element which is
away from the base.
31. The On-the-Move antenna of claim 28, wherein the beam forming
matrix comprises: four inputs; a sine pattern output; a cosine
pattern output; and an omni directional pattern output.
Description
FIELD OF THE INVENTION
One embodiment is directed to antennas, and more particularly
directed to direction finding antennas.
BACKGROUND INFORMATION
Radio direction finding is the process of electronically
determining the direction of arrival of a radio signal
transmission. The techniques for obtaining cross bearings of an
emitter and using triangulation to estimate target positions are
well-known. The ability to ascertain the geographical location of
an emitting transmitter offers important capabilities for many
modem communications applications, such as land, air, and sea
rescue, duress alarm and location, law enforcement, and military
intelligence. There are numerous direction-finding antennas and
systems in the prior art.
It is advantageous to design direction finding antennas that can
fit in small packages, especially where those direction finding
antennas are intended to be portable and used in the field.
However, it is difficult to build direction finding antennas for
small packages without sacrificing bandwidth, frequency response,
and signal detection quality.
SUMMARY OF THE INVENTION
Systems and methods in accordance with an embodiment are directed
to a HESA ("High Efficiency Sensitivity Accuracy")
direction-finding ("DF") antenna system. One embodiment is a
direction-finding antenna with electronics for receiving radio
signals in a frequency range of about 2 megaHertz to about 18
gigaHertz. The direction-finding antenna may include several
components for different frequency ranges. In one embodiment, one
component is an edge-radiating antenna comprising a first plate and
a second plate disposed parallel to each other and radiating into
open space, a concentric cylinder connecting the first plate to the
second plate, eight feed points disposed equally around the outside
of the concentric cylinder with eight feed lines extending from the
first plate to the second plate, and a shunt resistor across each
feed gap. The eight feed lines are electrically coupled to a beam
forming matrix that detects the direction of a beam.
In another embodiment, a component is a monopole array comprising
eight monopole elements connected to a first center mast. The
monopole array is disposed inside the concentric cylinder and
modified with resistors such that no resonance occurs. The eight
monopole elements are electrically coupled to a beam forming matrix
that finds a direction of a beam.
In yet another embodiment, a component is a dipole array comprising
eight dipole elements connected to a second center mast. Each of
the eight dipole elements is resistively loaded to increase
bandwidth, and the eight dipole elements are electrically coupled
to a beam forming matrix that detects the direction of a beam. The
second center mast may include a plurality of resistors disposed on
the mast to prevent resonance.
In yet another embodiment, a component is a biconical horn that
houses the edge-radiating antenna or dipole array. The biconical
horn comprises eight ribs connecting a top horn to a bottom horn.
The eight ribs are electrically coupled to a high impedance
resistor disposed at the center of the biconical horn. The top horn
and bottom horn of the biconical horn may include a base having an
aperture termination including resistors in shunt with each
other.
In yet another embodiment, the beam forming matrix includes eight
inputs, a sine pattern output, a cosine pattern output, and an omni
directional pattern output. The eight inputs include inputs A, B,
C, D, E, F, G and H, and the sine pattern equals (input C+input
D)-(input G+input H), the cosine pattern equals (input A+input
B)-(input E+input F), and the omni directional pattern is the sum
of the eight inputs. The sine, cosine, and omni directional
patterns are used to calculate a direction of arrival (period)
versus "a beam."
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 illustrates the mechanical layout of one dipole element of a
dipole array in accordance with an embodiment;
FIG. 2 illustrates a vertical cross section of a dipole array in
accordance with an embodiment;
FIG. 3. illustrates a horizontal cross section of dipole array in
accordance with an embodiment;
FIG. 4 illustrates a cross section of edge-radiating antenna in
accordance with an embodiment;
FIG. 5 illustrates a horizontal view of an edge-radiating antenna
in accordance with an embodiment;
FIG. 6A illustrates a modified Vivaldi structure in accordance with
an embodiment;
FIG. 6B illustrates a modified Vivaldi structure cross section view
in accordance with an embodiment;
FIG. 7A illustrates stacked biconical antennas in accordance with
an embodiment;
FIG. 7B illustrates stacked biconical antennas in accordance with
an embodiment;
FIG. 8 illustrates a block diagram of the beam finding matrix in
accordance with an embodiment;
FIG. 9 illustrates an On-the-Move antenna in accordance with an
embodiment;
FIG. 10 illustrates OMNI pattern angle data from an edge-radiating
antenna in accordance with an embodiment;
FIG. 11 illustrates OMNI pattern frequency gain data from an
edge-radiating antenna in accordance with an embodiment;
FIG. 12 illustrates OMNI pattern frequency deviation data from an
edge-radiating antenna in accordance with an embodiment;
FIG. 13 illustrates COSINE pattern angle data from an
edge-radiating antenna in accordance with an embodiment;
FIG. 14 illustrates COSINE pattern frequency gain data from an
edge-radiating antenna in accordance with an embodiment;
FIG. 15 illustrates COSINE pattern null depth data from an
edge-radiating antenna in accordance with an embodiment;
FIG. 16 illustrates SINE pattern angle data from an edge-radiating
antenna in accordance with an embodiment;
FIG. 17 illustrates SINE pattern frequency gain data from an
edge-radiating antenna in accordance with an embodiment;
FIG. 18 illustrates SINE pattern null depth data from an
edge-radiating antenna in accordance with an embodiment;
FIG. 19 illustrates OMNI pattern angle data from a modified Vivaldi
biconical antenna in accordance with an embodiment;
FIG. 20 illustrates OMNI pattern frequency gain data from a
modified Vivaldi biconical antenna in accordance with an
embodiment;
FIG. 21 illustrates SINE pattern frequency gain data from a
modified Vivaldi biconical antenna in accordance with an
embodiment;
FIG. 22 illustrates SINE pattern angle data from a modified Vivaldi
biconical antenna in accordance with an embodiment;
FIG. 23 illustrates SINE/COSINE null orthogonality data from a
modified Vivaldi biconical antenna in accordance with an
embodiment;
FIG. 24 illustrates COSINE pattern angle data from a modified
Vivaldi biconical antenna in accordance with an embodiment;
FIG. 25 illustrates COSINE pattern frequency gain data from a
modified Vivaldi biconical antenna in accordance with an
embodiment;
FIG. 26 illustrates COSINE pattern frequency gain data from an
On-the-Move ("OTM") antenna in accordance with an embodiment;
FIG. 27 illustrates OMNI pattern frequency gain data from an OTM
antenna in accordance with an embodiment;
FIG. 28 illustrates SINE pattern angle data from an OTM antenna in
accordance with an embodiment;
FIG. 29 illustrates SINE pattern frequency gain data from an OTM
antenna in accordance with an embodiment; and
FIG. 30 illustrates COSINE pattern angle data from an OTM antenna
in accordance with an embodiment.
DETAILED DESCRIPTION
Systems and methods in accordance with an embodiment are directed
to a HESA ("High Efficiency Sensitivity Accuracy")
direction-finding ("DF") antenna system that operates over a range
from 2 MHz to 18 GHz. The basic antenna comprises an upper plate
and a lower plate connected by a short circuit element. The feed
region is spaced out from the short circuit a specific distance
that enables the highest frequency of operation to produce an
omni-directional pattern when connected to a beam forming network
with a uniform amplitude and uniform phase distribution. The
distance between each of the feed elements is such that an
omni-directional pattern is achieved. The antenna may be circular
as may be the arrangement of the feeds. The antenna aperture may be
directly at the feed region or may be extended beyond the feed
region by a parallel plate region or biconical flare region.
The feeds are launched from the top or bottom of the feed region
and impedance matched to the antenna driving point impedance by
using one or more of the following techniques: series transmission
lines, shunt transmission lines, resistors placed in series with
feed elements, and resistors placed in shunt with feed elements.
The combination of techniques results in a highly sensitive feed
region with efficient transfer of fields from the feed region to
transverse electric and magnetic ("TEM") mode coaxial cable that
connects to a beam forming network.
Resistors may be placed on the feed elements to stabilize the
element impedance in electrically small antennas. The resistors may
also be placed in series on an element in strategic areas to
minimize higher order modes from propagating for bandwidth
extension. Typically, resistors in an array configuration have a
net value impedance (free space) around 377 ohms. For example, an
Altshuler antenna array may be an example where this value is
important. Instead, one embodiment here finds that in order to
achieve more gain and minimize losses, an appropriate resistor
value is a net value of 200-300 ohms/impedance range. Here, a total
value for a typical array of eight resistors would be in the
1600-2400 ohm range to net out 200-300 ohms (impedance), which
achieves more gain. For a 32 resistor array, for example, a total
of 6400-9600 ohm range will net out a resistor array impedance of
200-300 ohms. Unlike conventional systems, more gain is achieved
with a lower net ohms/impedance value in the resistors.
An antenna system may include multiple types of antennas operating
in different frequency ranges. In one embodiment, an antenna system
includes some or all of a dipole array, a monopole array, an
edge-radiating antenna, and a modified Vivaldi launch structure.
The components are connected to a beam forming matrix for
determining the direction of a signal.
Dipole Array
Typically, the usual elements for small antenna direction finding
antenna elements are dipoles or loop elements that have limited
bandwidths. In an embodiment, dipoles are modified by adding
resistors near the ends of the elements to pull up the input
impedance. This increases the bandwidth to approximately 3:1. To
increase the bandwidth even further, a second resistive termination
located one half of a wavelength away may be added, the wavelength
being determined by the desired highest frequency of operation.
This increases the bandwidth to 5:1. Each additional resistive
termination will increase the bandwidth to 7:1, 9:1, and so on. For
very short dipoles at extremely low frequencies, resistors may be
placed across the feed point to stabilize the driving feed point
impedance to a level where the radiation resistance of the antenna
is raised to a level where impedance matching can occur. There may
be a tradeoff in efficiency vs. impedance, however. Efficiency is
lost at the high end of the frequency band, while impedance
stabilization is achieved at the lowest frequencies for uniform
power transfer.
FIG. 1 illustrates the mechanical layout of one dipole element of a
dipole array in accordance with an embodiment. In this example,
dipole element 100 is 57 cm long with a balun box 101 disposed at
the middle of dipole element 100. A resistor 102 is disposed 3.75
cm from the end of dipole element 100, with a second resistor 103
disposed 7.5 cm from the center of resistor 102, and a third
resistor 104 disposed 7.5 cm from the center of resistor 102. A
mirror image is made on the other side of balun box 101 with
resistors 105, 106, and 107, respectively. In one embodiment, the
impedance of resistors 102-107 is 200-300 Ohms. This type of dipole
element is then arrayed around a cylinder or mast using eight such
elements.
FIG. 2 illustrates an end view of a dipole array 200 in accordance
with an embodiment. Dipole elements 201-208 correspond to a dipole
element such as dipole element 100. In one embodiment, these dipole
elements 201-208 are spaced approximately a 1/4 wavelength at the
highest frequency of operation away from cylinder 209, and about
1/2 wavelength apart on the circumference so that when connected to
a beam forming matrix (discussed infra), the direction finding
patterns of omni, sine and cosine are formed. FIG. 3. illustrates a
horizontal view of dipole array 200 in accordance with an
embodiment. In this view, dipole elements 208, 201, 202, 203, and
204 are shown, whereas dipole elements 205-207 are not visible from
this angle. Dipole element 202 is shaded to differentiate it from
cylinder 209. Cylinder 209 further includes resistors 301-304
decouple the dipole elements 201-208 to eliminate unwanted current
resonances on the antenna body.
Edge-Radiating Antenna
FIG. 4 illustrates a cross section of edge-radiating antenna 400 in
accordance with an embodiment. Edge-radiating antenna behaves like
an edge slot antenna because the signals radiate from the edge of
the antenna. The edge-radiating antenna is formed by two plates, an
upper plate and a lower plate (not shown), tied together by a
concentric cylinder 401 to form a short circuit. Edge-radiating
antenna 400 may be modified for two band operation by adding a
circular array of eight monopoles 402-409 in an array with a center
mast 410 modified so no resonance occurs on the upper plate. These
monopole outputs are then connected to a beam forming network
(discussed infra) to obtain the omni, sine, and cosine direction
finding antenna patterns. FIG. 5 illustrates a horizontal view of
edge-radiating antenna 400. This view demonstrates that there is a
resistor 505 disposed at the end of each of the monopole elements,
for example, 402. Furthermore, this view demonstrates that there
are eight feed points at the outside edge of cylinder 401 with a
feed line 501 extending from the bottom edge to the top edge for
each feed point. Feed point impedance is stabilized by adding left
shunt resistor 502 and right shunt resistor 503 across a feed gap
in the feed region. With this configuration, a bandwidth in excess
of 20:1 may be achieved.
Modified Vivaldi Biconical Structure
In an embodiment, an antenna may be modified by adding biconical
flares to increase the bandwidth even further. In one example, a
bandwidth of 100:1 may be achieved at the lowest frequency of
operation where the aperture is 3% of a wavelength. Edge
termination is applied to the outer edges of biconical flares to
achieve this wide bandwidth, along with feed structure
improvements. Feed structure improvements include modification of
the Vivaldi rib taper and adding a resistor to the rib termination,
replacing the short circuit normally used. Also, a ferrite bead is
added through the center to allow cables to pass through from top
to bottom.
A typical Vivaldi launch is modified to operate below its normal
cutoff frequency. The matching network is changed from a short
circuit to using a high impedance resistor to replace the short
circuit. This allows fields to propagate into the biconical
section. The vertical height of the structure is approximately one
foot, therefore an aperture termination strip using resistors in
shunt with each other and spaced around the top and bottom allows
the waves to propagate in and out without mismatches. At the high
end of the band (30 Mhz to 3 Ghz), the resistors on the aperture
are not seen by the propagating wave. The feed system is arranged
internally so that the eight elements provide direction finding
information to the matrix.
FIGS. 6A and 6B illustrates a side view and a cross section view,
respectively, of a modified Vivaldi structure 600 in accordance
with an embodiment. A first resistor ring array 601 and second
resistor ring array 602 comprise low frequency resistor arrays that
attach to the biconical horns 603 and 604. Biconical horns 603 and
604 each include eight launching ribs 605 in a radial placement at
the top of each horn 603 and 604. Each launching rib 605 includes a
feed point 606 across the rib 605, which connects to the matrix via
a coaxial connection. The upper cone is a mirror image of the lower
cone except the coaxial inputs in the lower cone ribs are short
circuits in the upper cone ribs. Each rib 605 connects to a
resistor in a third resistor array 607 that is disposed between
horns 603 and 604 and around an epoxy glass cylinder 608 housing a
ferrite cylinder 609. Third resistor array 607 replaces the short
circuit in a typical Vivaldi element and thus allows the field to
propagate in the biconical structure.
In another embodiment, bicones can also be stacked vertically as
shown in FIG. 7A (measurements in inches). A broader band of
coverage can be achieved according to an embodiment by vertically
stacking a plurality of biconical antennas, e.g., 701 and 702. Each
antenna would have a mode former to which the plurality of feed
elements is connected, as previously discussed herein. In one
embodiment, biconical antennas 701 and 702 are stacked in
conjunction with edge-radiating antenna 703, previously described
with reference to FIGS. 4 and 5. FIG. 7B illustrates another
embodiment in which biconical antennas 701 and 702 are stacked in
conjunction with a stacked Modified Vivaldi array 705, previously
described with reference to FIGS. 6A and 6B, and further in
conjunction with a dipole array antenna 707, previously described
with reference to FIGS. 1-3. In one embodiment, high frequency
direction finding component 709 is also included. Vertically
stacking a plurality of such antennas provides direction-finding
accuracy over a broad frequency range, since each antenna is
designed to accommodate a particular frequency range.
Direction Finding Matrix
In one embodiment, the beam forming network for a circular
direction finding array consists of 8 antenna array elements on the
input and three antenna patterns at the output. The input array
element patterns are equal amplitude and circularly disposed around
the array. The input array elements may be dipoles, monopoles,
Vivaldi elements, or any other type of element suitable for
summing.
The output antenna patterns are omni, sine, and cosine patterns.
The omni pattern is the sum of all 8 elements. The sine and cosine
patterns are the difference of opposed sums of elements (opposite
pairs), as explained below. The sine and cosine patterns provide
for angularly offset patterns in amplitude and phase, whereas the
omni pattern is of uniform amplitude and phase about the circular
array.
Instead of the 4.times.3 beam finding matrix typically used, this
embodiment includes an 8.times.3 matrix. The sine, cosine, and omni
outputs allow the voltage vectors to analyzed to determine
direction of arrival. Information appears at each port of the
matrix instantaneously. Thus, the matrix can find signals that are
only on for short periods of time. This embodiment does not need to
store information to process the signals for direction finding.
FIG. 8 illustrates a block diagram of the beam finding matrix in
accordance with an embodiment. Elements A-H represent the circular
array of 8 antenna elements, where the angle of elements A-H is as
follows: A=0.degree., B=45.degree., C=90.degree., D=135.degree.,
E=180.degree., F=225.degree., G=270.degree., and H=315.degree..
Elements A and B are summed by power divider 801, elements E and F
are summed by power divider 802, elements C and D are summed by
power divider 803, and elements G and H are summed by power divider
804. Next, 0/180 hybrid element 805 produces a sum and delta
(difference) signal for the A+B signal and the E+F signal, the
delta of which is the cosine pattern COS=(A+B)-(E+F). This produces
a null position halfway between signals, i.e., 180.degree.. Then,
0/180 hybrid element 806 produces a sum and delta signal for the
C+D signal and the G+H signal, the delta of which is the sine
pattern SIN=(C+D)-(G+H). This produces a second null position
halfway between the other null position, thus creating a 90.degree.
space. The sum signals of the 0/180 hybrid elements 805 and 806 are
then summed by power divider 807 to produce the omni pattern
OMNI=(A+B)+(E+F)+(C+D)+(G+H). The magnitude indicates the direction
and the phase indicates the quadrant, thus allowing direction
finding.
On the Move ("OTM")
Typical OTM antennas use monopole elements. In this case, whatever
the OTM antenna is mounted on becomes part of the antenna. In one
embodiment, monopoles are made to look like dipoles electrically so
that the object the OTM is mounted on is no longer part of the
antenna. An OTM in accordance with this embodiment may be mounted
on a vehicle, boat, or aircraft. An OTM in accordance with this
embodiment may operate at 30 MHz, while only being 31 inches in
length.
FIG. 9 illustrates an OTM antenna 900 in accordance with an
embodiment. OTM antenna 900 includes dipole elements 901, 902, and
two other dipole elements that are not shown in this view. Dipole
element 901 is shown in cross section, while dipole element 902 is
show as an exterior view. The dipole elements include a feed point
903 located 26 inches from base 904. A large ferrite 905 is located
at the base 904. In one embodiment, a resistor insert 906 is
located approximately 7 inches from base 904. A small ferrite 907
is disposed between resistor insert 906 and matching section 908.
In one embodiment, a second resistor insert is located
approximately 2 inches from the end of dipole 901. The dipole
elements feed into a 4.times.3 direction finding matrix 910. By
adding the ferrites and suppressing currents in the base 904 and
cables (not shown), the antenna impedance is isolated. This method
of isolation allows for a much shorter height than OTM antennas of
the prior art.
Experimental Data
FIGS. 10-3 illustrate example pattern data acquired from various
embodiments of antennas discussed above. FIG. 10 illustrates OMNI
pattern angle data from an edge-radiating antenna such as
edge-radiating antenna 400 discussed above. FIG. 11 illustrates
OMNI pattern frequency gain data from an edge-radiating antenna
such as edge-radiating antenna 400 discussed above. FIG. 12
illustrates OMNI pattern frequency deviation data from an
edge-radiating antenna such as edge-radiating antenna 400 discussed
above. FIG. 13 illustrates COSINE pattern angle data from an
edge-radiating antenna such as edge-radiating antenna 400 discussed
above. FIG. 14 illustrates COSINE pattern frequency gain data from
an edge-radiating antenna such as edge-radiating antenna 400
discussed above. FIG. 15 illustrates COSINE pattern null depth data
from an edge-radiating antenna such as edge-radiating antenna 400
discussed above. FIG. 16 illustrates SINE pattern angle data from
an edge-radiating antenna such as edge-radiating antenna 400
discussed above. FIG. 17 illustrates SINE pattern frequency gain
data from an edge-radiating antenna such as edge-radiating antenna
400 discussed above. FIG. 18 illustrates SINE pattern null depth
data from an edge-radiating antenna such as edge-radiating antenna
400 discussed above.
FIG. 19 illustrates OMNI pattern angle data from a modified Vivaldi
biconical antenna such as modified Vivaldi biconical antenna 600
discussed above. FIG. 20 illustrates OMNI pattern frequency gain
data from a modified Vivaldi biconical antenna such as modified
Vivaldi biconical antenna 600 discussed above. FIG. 21 illustrates
SINE pattern frequency gain data from a modified Vivaldi biconical
antenna such as modified Vivaldi biconical antenna 600 discussed
above. FIG. 22 illustrates SINE pattern angle data from a modified
Vivaldi biconical antenna such as modified Vivaldi biconical
antenna 600 discussed above. FIG. 23 illustrates SINE/COSINE null
orthogonality data from a modified Vivaldi biconical antenna such
as modified Vivaldi biconical antenna 600 discussed above. FIG. 24
illustrates COSINE pattern angle data from a modified Vivaldi
biconical antenna such as modified Vivaldi biconical antenna 600
discussed above. FIG. 25 illustrates COSINE pattern frequency gain
data from a modified Vivaldi biconical antenna such as modified
Vivaldi biconical antenna 600 discussed above.
FIG. 26 illustrates COSINE pattern frequency gain data from an OTM
antenna such as OTM antenna 900 discussed above. FIG. 27
illustrates OMNI pattern frequency gain data from an OTM antenna
such as OTM antenna 900 discussed above. FIG. 28 illustrates SINE
pattern angle data from an OTM antenna such as OTM antenna 900
discussed above. FIG. 29 illustrates SINE pattern frequency gain
data from an OTM antenna such as OTM antenna 900 discussed above.
FIG. 30 illustrates COSINE pattern angle data from an OTM antenna
such as OTM antenna 900 discussed above.
While several embodiments of the invention have been described, it
will be understood that it is capable of further modifications, and
this application is intended to cover any variations, uses, or
adaptations of the invention, following in general the principles
of the invention and including such departures from the present
disclosure as to come within knowledge or customary practice in the
art to which the invention pertains, and as may be applied to the
essential features hereinbefore set forth and falling within the
scope of the invention or the limits of the appended claims.
* * * * *